The experiments reported in this paper and in the preceding one indicate that with a given susceptible mouse population and a certain strain of mouse typhoid bacilli the sporadic and epidemic prevalences of mouse typhoid are determined by the spacial and quantitative distribution of the bacilli. Under circumstances in which the entire mouse population is so exposed as to be in direct contact with an infecting dose of the mouse typhoid bacillus, the nature of the resulting mortality curve depends upon the quality of susceptibility of the individuals composing the population.